Three arches on one span
Each flank is an arc swung from a pin on the springing line. With the pins on the springing points the arch is equilateral and rises 0.866 of its span; move them outward and it becomes a lancet, here 1.000; move them inward and it drops to 0.707. Arches set out this way carry the ambulatory of Saint Denis, built 1140 to 1144.
In the faith
Abbot Suger, who built that ambulatory, wrote that the church would shine with the wonderful and uninterrupted light of its windows, and on its doors he set verses saying that the dull mind rises to the truth through material things.
Sources
- Abbot Suger, De consecratione, chapter IV
- Abbot Suger, De administratione, chapter XXVII
- Basilica of Saint Denis, ambulatory, 1140 to 1144